1. Field of the Invention
The present invention relates to tethers, more particularly, to expandable tethers for securing boats and the like.
2. Description of the Related Art
The elastic tie down is a well-known device developed to restrain an object from moving away from a another object, for example, a boat from a dock. Elastic tie downs permit some relative movement between the restrained objects so that small relative motions can be accommodated without creating large stresses and damage to the restrained objects.
To prevent overstressing the tie down to the breaking point, it is known to combine a limiting component with an elastic component. The elastic component provides resilient restraint against separation, and the limiting component remains slack. When the separating force reaches a predetermined value, the elastic component becomes stretched such that the limiting component is taut and prevents further stretching of the elastic component. Examples of such tie downs are disclosed in U.S. Pat. Nos. 1,296,057, 2,991,524, and 4,694,541. The main shortcoming of these tie downs is their bulk. The elastic component is an elastic tube through which the limiting component, such as an inelastic rope, extends. When there is no separating force on the tie-down, the rope is bundled haphazardly within the tube, meaning that the tube must be several times the thickness of the rope, depending upon the amount of stretch permitted.
In an alternate construction, the elastic component forms a core to a braided line, the limiting component. When the elastic component is not stretched, the braided line is compressed. Since the line is not bundled, the tie down is thinner than the tie downs with the internal limiting component. However, since the braid on the line is a cross-hatch of threads, it is not smooth and easy to snag, particularly in the unstretched condition.